Copolymers of the type produced by the process of the present invention were first described in U.S. Pat. No. 3,838,108, owned by the Assignee of record herein. That patent taught the anionic polymerization of olefins and other monomers which were then end-capped with isocyanates or isothiocyanates. Typically, the olefin selected was butadiene and once end-capped, it was then reacted with other monomers, namely nylon forming or lactams containing at least three carbon atoms in the lactam ring. The resulting nylon block copolymers retained the favorable characteristics of the nylon such as good impact strength, good abrasion resistance and low coefficients of friction. Unexpectedly and additionally, they possessed the processing characteristics of the base polymer which in the case of the polybutadienes, meant milling and processing at ambient temperatures. Furthermore, they could be molded as plastics or as rubbers and at temperatures below the melt temperature of the nylon.
The only attendant problem possessed by these copolymers was that they exhibited cold flow. A substance is said to cold flow if a quantity of it will gradually flow or spread itself out over a flat surface even though it is normally a solid and will retain a given shape for a short period of time.
In U.S. Pat. No. 4,070,344, also owned by the Assignee of record, a similar procedure was initially followed through the end-capping step of the polybutadiene or other base polymer with a polyisocyanate or polyisothiocyanate. This polymer was then reacted with compounds containing an amide, such as a lactam, to give an imide type end group, which was subsequently hydrolyzed to form a stable amine terminated polymer which could itself be used or stored for an extended time and then reacted with other monomers to provide various block and graft copolymers. Exemplary monomers include amides, ureas, urethanes, imides and the like. These materials possessed useful polymer properties but also exhibited cold flow.
In a co-pending application, owned by the Assignee of record, a solution polymerization was set forth for the preparation of free flowing pellets of cold flowing rubber. The process included the steps of preparing in suspension the tacky, cold flowing polymer in the presence of a solution of non-cold flowing rubber to form a product, removing the suspension solvent, pelletizing and then subjecting the pellets to a surface treatment to remove tack.
With the exception of the co-pending application, it has not been possible heretofore to eliminate cold flow and tack from cold flowing rubber and copolymers. However, the latter process does not provide for the rapid bulk polymerization of the component monomers. In addition to the speed of the present process, there is also no necessity of solvent removal.